What is Four Quadrant Control?

Hardware: Motion Control

Problem:What are the four quadrants of operation of a motor drive? How does this apply to my motion control system?

Solution:To answer this question, we must understand a little about the purpose of servo motors and their function as an electromechanical conversion device. Servo motors are differentiated from other types of electric motors by the fact that they are typically designed with an emphasis on smooth, accurate position and/or velocity control, rather than ultimate power output. Servo systems are often bi-directional (CW or CCW), whereas many common industrial motor drives for pumps and fans and similar equipment only operate in one direction. Accurate control of acceleration and deceleration of a motor is another characteristic of servo systems, which is not always found in simple motor control systems. Many motors rely on the friction alone to decelerate the load when power is removed.

If we consider both directions of operation (CW and CCW) and both modes (acceleration and deceleration), we arrive at four distinct areas, or quadrants, of operation. This can be visualized by plotting the velocity of the motor on the X axis of a graph and the direction of applied torque on the Y axis as shown below. Quadrants 1 and 3 represent the motor applying torque in the direction of motion, while quadrants 2 and 4 represent applying torque opposite the direction of the motion. In quadrants 1 and 3 the flow of energy is from electrical to mechanical. The servo motor is converting electrical power from the drive into motion in the system. In quadrants 2 and 4, the motor is actually acting as a generator. The motion of the system is being converted into electrical power, which is then absorbed by the drive.

Some motor drives are capable of operating in only quadrant 1, while others will work in quadrants 1 and 3, quadrants 1 and 4, etc. Since most servo drives are designed for accurate control in both directions, many will operate, at least transiently, in all for quadrants. To do this the drive must be able to both source and sink electrical power from the motor.